The correct answer is 'C'. For read-heavy workloads, using Amazon RDS read replicas is the most effective way to achieve high read performance. Read replicas distribute the database read operations, which significantly improves read scalability and performance. Multi-AZ deployments are mainly used for high availability and failover but do not improve read performance. Using open-source replication software on an EC2 instance would involve more effort compared to utilizing managed read replicas in RDS.